From the Amateur Transplants, the same people who did London Underground.
There album is f*cking hilarious by the way - I recommend it. They have a DVD out as well which is just as good if not better.
A good few of there songs are medically related as they are doctors afterall, but a good chunk are understandable to non-medics! (like the Shelia's Wheels one! "The NHS Song" is also a cracking tune - in the style of the THe JCB song from a few years ago)
http://www.amateurtransplants.net/